Under-water spraying

ABSTRACT

The described invention relates to a method and apparatus for applying paint or the like to a submerged surface and includes the provision of a hollow shield with an elongated opening which shield is purged of water by compressed air the resultant airfilled space being traversed by a sheet-like spray of the paint supplied from atomising means and formed so as to be substantially uninterrupted by the internal wall of the shield. Various systems are described by way of elaboration of the actual margin of the shield to accommodate different surfaces; to provide for maintaining appropriate spacing between the margin of the shield and the surface and for affording mobility of the whole apparatus.

United States Patent 11 1 Tusch et a1.

[451 Feb. 25, 1975 1 1 UNDER-WATER SPRAYING [73] Assignee: ColebrandLimited, London,

England 22 Filed: Aug. 27, 1973 21 Appl. No.2 391,714

Related US. Application Data [62] Division of Ser. No. 174,445, Aug. 24,1971, Pat. No.

[52] US. Cl 117/104 R, 29/81 K, 114/222 [51] Int. Cl. B05c 5/02 [58]Field of Search 114/222, 221 R; 15/322,

l5/1.7', 29/81 B, 81 K, 81 C; 117/104 R, 127; 118/50, 305, 207; 134/37,198, 199; 51/11, 319; 239/290, 288.5

3,609,916 10/1971 Hammelmann 114/222 3,766,879 10/1973 Jones 114/222FOREIGN PATENTS OR APPLICATIONS 1,454,007 10/1965 France 114/222 PrimaryExaminerGeorge E. A. Halvosa Assistant ExaminerCharles E. FrankfortAttorney, Agent, or FirmAllison C. Collard [57] ABSTRACT The describedinvention relates to a method and apparatus for applying paint or thelike to a submerged surface and includes the provision of a hollowshield with an elongated opening which shield is purged of water bycompressed air the resultant airfilled space being traversed by asheet-like spray of the paint supplied from atomising means and formedso as to be substantially uninterrupted by the internal wall of theshield. Various systems are described by way of elaboration of theactual margin of the shield to accommodate different surfaces; toprovide for maintaining appropriate spacing between the margin of theshield and the surface and for affording mobility of the wholeapparatus.

14 Claims, 12 Drawing Figures PATENTEU FEB 2 5 ms SHKEI 1 BF 5PATENTEUFEB25|915 3.868288 sum u (if 5,

UNDER-WATER SPRAYING This is a division of application Ser. No. 174,445filed Aug. 24, 1971 now issued as US. Pat. No. 3,788,273.

This invention relates to a method of applying paint or like liquid to asurface which is submerged, and the apparatus used to practise themethod. The invention is primarily intended to be used in the paintingof, or application of a liquid in paint-like manner to, the hull of aship or any other submerged surface which is normally inaccessibleexcept to a diver. Particularly in the case of modern very large shipsfor which docking facilities are not easily available they neverthelessrequire to be treated with compositions such as for corrosion or foulingprotection from time to time. There are also instances when it isrequired to apply similar substances to the submerged part of a sea-wallor like fixed structure, or to moored buoys.

The invention is entirely concerned with spray painting, or equivalentapplication (which we will refer to for brevity as painting) that is tosay painting by the projection or droplets of the paint withconsiderable velocity to impact the surface upon which the droplets thencoalesce to form a uniform film. It has been proposed previously to useas an applicator a bell-like shield enclosing a spraying nozzle and topurge the interior of the bell by compressed air so that the paint canpass relatively freely through air in the bell finally reaching thesurface. In such prior proposals, however, it does not seem to have beenthought practicable to apply the foregoing general idea in an economicand sensible manner and, which is more important, to cover the requiredsurface area quickly by painting in a relatively broad swath or band byjust one passage of the spray. If a circular shield be used aspreviously proposed, the length of its margin (i.e. the lineardimension) is unneccessarily great in proportion to the enclosed volumeof the shield, so that the maximum leakage of air, and therefore themaximum consumption of air, can occur. The present invention seeks toeconomise in air to be supplied and as a secondary advantage of sucheconomy, to diminish the cloud of bubbles which inevitably escape andcan impede the operators view of his work. A major advantage of thepresent invention therefore resides in its economy and convenience ofoperation.

The invention also makes use of various practical expedients which'mayor may not be applied according to the scale of the operation. Forexample, if large and heavy spraying apparatus is to be used as might bethe case for very large ships sides, the invention provides for means tosecure the apparatus to the surface to be treated in such a manner thatit can easily be moved, and also so that in any one attached position aconsiderable area may be painted. Again, if the apparatus is to behand-held means are provided by the invention whereby it can easily bemoved about over the surface. yet again, since it is required to controlwith considerable exactness the gap between the shield and the surfacethrough which gap the air is to escape, the invention provides means formaintaining and controlling the gap. Since such means involve contactbetween the surface and parts which move over the surface, the inventionprovides that such contact is avoided in the area which has just beenpainted so that the newly applied paint is not disturbed. The means foreffecting this according to the invention are reversible so that changeof sense of direction of the painting operation is provided for. Theinvention affords other practical devices which have been found to beadvantageous in some cases of submerged painting operations. Theinvention is in the first instance intended to be practised by a diveroperator but it will not require very much elaboration to enable it tobe used as a fully automatic applicator device.

Basically then, the invention resides in a method of coating a submergedsurface by spraying with a liquid, in which there is passed over thesurface the margin of an opening which is of relatively short dimensionin the direction of such passage and of relatively long dimension in thedirection across such passage, maintaining the margin so that at leastits trailing edge (i.e. that of longer dimension which, in relation tothe sense of direction of passage, is behind the other) is spaced fromthe surface by a gap which leads from the opening of an otherwisewatertight hollow shield; supplying into the shield compressed air at asufficient pressure and rate to keep the interior of the shield purgedof water whilst there is air escape through the gap, and projecting theliquid to the surface from a source which is inside the shield andspaced from the surface as a spray of droplets in a sheet-like patterncorresponding in short and long dimensions to the opening but smaller,the velocity of projection of the droplets and their mass being suchthat they or at least a majority of them penetrate the volume ofintervening air maintained within the shield and such film of water asthere may be on the surface so as to reach the surface and form thereona continuous film.

The invention further includes the elaboration of the foregoing methodby various other steps as defined in the claims herewith.

The invention also includes apparatus for performing the above methodand its variations. in particular, ap-

paratus for painting a submerged surface comprises a hollow, watertightshield of a shape which, in a crosssection, extends from the location ofa spray jet to an opening which is of considerably greater length thanbreadth, the length being transverse to the intended direction ofpassage for painting, and the spray jet is of any suitable known kindfrom which is ejected a spray of droplets of a flat or sheet-likecharacter; and the shape of the shield is such as to surround this sprayso as effectively not to obstruct the spray. Further features of theapparatus will become clear from the following descriptions and from thesubject of Claims.

in applying the invention it is preferred to use a spray of purelyhydraulic type, that is to say an airless spray in which the paint isdelivered at a high pressure and from which the paint emerges at veryhigh velocity and breaks up into droplets after emerging. it is,however, possible to use an air type spray but in such case the airwhich, as will be seen below, is used to purge the shield of water, willprobably have to have a certain velocity itself, so as not to impede theaction of the airspray. Yet again it is possible to make use ofelectrostatic spraying providing'that the interior surface of the shieldis electrically isolated from the paint source either by virtue of aninsulating coating or by an insulating separator between the gun and theshield thus preventing the spray being attracted to the shield insteadof to the surface to be painted. For various reasons of conveniencehowever, the invention is primarily concerned with simple hydraulicspray means and there are many variations of appropriate spray nozzleson the market which produce the required spray pattern in the form ofathin sheet: as will be seen, the spray means may consist of a pluralityof aligned spray nozzles collectively delivering a sheet of sprayparticles.

Apparatus according to the invention, with comments on its use, will nowbe described by reference to the accompanying drawings in which:

FIG. 1 is a plan view of the so-called spraygun constituting theeffective apparatus.

FIG. 2 is a part section on the line XX in FIG. 1,

FIG. 3 is an end elevation (from the same aspect as FIG. 2) of the spraygun shown in greater detail and FIG. 4 is a plan view of the gun asshown in FIG. 3 illustrating a modification intended to prevent bubblesfrom obscuring the divers view.

FIG. 5 is a sketch illustration showing a plurality of aligned spraynozzles.

FIGS. 6 and 6a are diagrams of another modification of the shield, todeal with certain types of surface e.g. where the surface is of steelsheets with lap joints.

FIG. 7 illustrates how castoring wheels may be used.

FIG. 8 is an illustration of a way of moving the spray gun over thesurface in a mechanised manner.

FIGS. 9 and 9A are diagrams to show an elaboration of the shield toeconomise in air and reduce bubbling.

FIG. 10 discloses a plurality of shields each with spray nozzle and airsupply means.

The gun forming the subject of this example is intended for use in spraypainting under water of substantially vertical surfaces (indicated at 10in FIG. 2), such as the sides of a ship. This gun in its simplest form,is intended to be hand-held and passed up and down the surface to bepainted, traversed transversely at the end of the up stroke, passedthrough a down stroke, again traversed, and so on.

The gun comprises a hollow shield 11 of generally fish-tail shape andinternally provided with a spray nozzle 12 at the closed, narrow, end ofthe shield. This nozzle is of a known type such as to produce by airlessatomisation, a divergent sheet-like spray of droplets conforming to theshape of the shield but sufficiently smaller in cross section tosubstantially avoid coating the internal surfaces of the shield. Thesesurfaces are preferably covered with P.T.F.E. as a further precautionagainst lodging of the paint on the surfaces or to make easier theremoval of any paint which has fouled the interior of the shield.Surrounding the closed end of the shield is a chamber 14 with an inlet15 for compressed air. Perforations 16 in the wall of the shield leadfrom the chamber 14 to an inner chamber 18 defined by a baffle 19. Thereis an annular gap 20 between the baffle 19 and the housing for thenozzle 12,

so that the air flow passes from the chambers 14 and 18 into the shieldaround the spray jet and out of the opening 22 of the shield, whichopening is narrow in the direction of intended passage and comparativelywide across such direction. The air supply arrangement is intended toadmit the air into the shield without disturbing the spray pattern.

The margin 22A of the mouth 22 lies in a plane making an angle of about45 with the axis of the nozzle 12 and, in use, is spaced at a smalldistance from the surface 10 to be sprayed. Provision is made, as willbe seen, to enable this distance to be adjusted to an optimum for theparticular surface being sprayed. When the nozzle axis lies in avertical plane and at an angle of about 45 to the surface 10, thegreater dimension of the mouth 22 then lies horizontally, the lesserdimension h (FIG. 1) then lying in the intended direction of movement ofthe gun. The rate and pressure of air supply into the shield ismaintained at a value sufficiently above the pressure of the ambientwater to purge the shield of water and keep it purged, so to exose thearea of the surface 10 within the margin 22A for painting. It is anadvantage of the construction described, however, that'if for any reasonwater enters the shield (e.g. because the gun runs off the surface beingpainted) or the air is interrupted, it will only do so to the level ah(FIG. 2) and the volume of water to be removed at the re-start of workwill be small. In that sense the shield acts as a diving bell."

The gun is mounted on a carriage 30, only partly shown in the drawings.This carriage has two wheels 31 at one side of the mouth 22 which run onunpainted parts of the surface 10 to the side of the mouth 22. Inaddition there are two wheels 32 which lie within the width of mouth 22and are alternatively engageable as shown in FIG. 3 by means of a doubleacting pneumatic ram 36, the piston rod 37 of which is connecteddirectly to the mounting for one wheel 32 and through a rocker 38pivoted on the shield to the mounting for the other wheel. When the gunis moving upwardly the upper wheel is engaged with the unpainted part ofsurface 10 as shown and the lower wheel 32 is held off the newly paintedarea of the surface. Conversely when the gun is moving downwardly theupper wheel is held off the surface and the lower wheel engages thesurface. The line of the force with which the spray gun is up plied tothe surface lies within the triangle formed by the contact points of thethree wheels, thus giving a stable arrangement.

The carriage may also be provided with a propeller (not shown) whichrotates about an axis perpendicular to surface 10 and so produces athrust tending to maintain the wheels 31, 32 in contact with the surfaceand hence maintain the mouth of the shield at its desired distance fromthe surface being sprayed.

The propeller and, for traction, the wheels 31 (and- /or 32) may bedriven by electricity, compressed air or hydraulically, the same powersource being used for both, if desired. Preferably the drive to thetraction wheels, if provided, is reversible. The speed at which thewheels and/or the propeller are driven may be variable and means may beprovided to maintain the speed at a predetermined value.

The nozzle 12 is mounted in a housing 34 providing a feed conduit forthe paint. This housing is mounted on the shield by way of a partspherical bearing 35 which enables the direction of the spray within theshield to be adjusted so that the spray may be caused to lie centrallyin the margin of the shield.

Means such as an interconnection between a paint supply valve and thepressure of the ram 36 may be provided for automatically cutting off thesupply of paint during periods in which the direction of movement of thegun is being reversed and wheels 32 changed over.

There may be a regulator for the air pressure within or attached to theshield. This may comprise a diaphragm (or equivalent piston) open on oneside to the ambient water pressure and operable to maintain the airpressure within the shield at a pre-set value above the ambientpressure.

It is to be appreciated that by employing a high ratio of width toheight (h) of the opening 22 not only is a relatively wide strip paintedat each up or down traverse of the gun but also the difference in waterpressure at the upper and lower edges of the mouth is reduced to aminimum which assists in maintaining displacement of the water with aminimum of expenditure of air. It is also an advantage that the mouth ofthe shield may be held close to the surface being painted which reducesthe consumption of air. However, a major advantage of keeping the lesserdimension (h) of the opening as small as is practicable is that thisaffords the least possible length (in linear terms) of margin 22A inrelation to the contained volume in the shield, thus affording the leastpossible leakage-path for the air.

It is within the invention to provide a deflector 39 as shown in FIG. 4above the mouth of the shield, to be held close to the surface beingpainted and sloped or shaped to divert to one side (or both sides) airbubbling up from the shield mouth, hence to reduce obstruction by thebubbles to visual inspection of the surface which has been, or is aboutto be, painted.

Also, one or more scrubbers may be provided to scrub the surface priorto application of paint. The scrubbers may be separate from or embodiedin the gun. These may be rotary brushes, driven by electricity,compressed air or hydraulically, and there may also be provided meansfor feeding at a controllable rate a wetting agent or other cleaningmaterial through the centre of the brush.

In FIG. 5 it is shown that three separate nozzles 51, 52 and 53 are usedwithin one shield 54. In such a case the actual shape of the shield maybe modified somewhat in the manner drawn so as to accommodate the threedroplet sprays indicated approximately in dotted line at 55. The sprayswill be so positioned and the pattern of their tips so selected thatthey overlap as at 56; this, if appropriately selected, will not resultin any undue concentration of paint in the zone 56 because the extrememargins of the divergent spray are in any case somewhat attenuated ascompared to the main part of the spray. It will be clear from thisillustration that any reasonable number of nozzles may be used, thebreadth to length proportion of the openingof the shield 54 of coursebeing appropriately varied. Moreover, instead of putting several spraynozzles, within one shield the apparatus may involve the provision ofseveral complete units of shield plus nozzle and these may be arrangedin somewhat staggered relationship so that one passage of the group ofshields produces a uniform swath of paint.

FIGS. 6 and 6A illustrate a device which copes with a particular problemencountered in painting some ships hulls or like structures. The deviceis one which adapts a shield to conform reasonably well with a certaintype of contour of surface. The same device enables a flat surface to bepainted. In FIG. 6 the surface to be painted is broken up into an area60A and a second area 60B these being supposed to be interconnected by alap joint 61 probably by welding at 62. The shield 63 of the apparatushas at the margin of its opening two parts, 64 and 65 which are attachedto the shield 63 by parallel links such as 66. Each of these parts canbe swung by virtue of the parallel links so that, for example, the part64 being swung the shield opening has its effective margin now shaped soas substantially to match the form of the weld 62. The operator will ofcourse move either 64 or into the appropriate position for theparticular circumstance encountered, in other words as is seen in FIG.6A, he can select the hand of operation. In FIG. 6A the part 65 isswung, part 64 being in the retracted position. Mechanism not shown inthe drawing may be provided in any suitable form to advance a guidewheel 67 to maintain the shield parallel to the surfaces being painted.The shield is conditioned for normal use on a flat surface by retractingboth parts 64 and 65 and placing the wheel 67 in the position to producea small and uniform gap between the margin of the shield and the surfacebeing painted. Similar provision, i.e. movable margin elements, may beused to facilitate operation over lines of rivets or similarexcrescences.

Moving now to FIG. 7, it is indicated diagrammatically how the carriage,which is to be seen more fully in FIGS. 1-4 and its side running wheelscan be arranged so that the operator can more readily traverse theappratus from one completed path to a second adjacent parallel path, orto accommodate his operation to various surfaces or around obstacles. Inthis Figure, 30 again indicates the side part of the carriage and thetwo wheels (31 in previous Figures) are now indicated at 70 and they aremounted like furniture castors on ,pivotal axes 71 providing for 360directional orientation of the wheels 70. The wheels 32 (earlierFigures) not shown in FIG. 7, will likewise be mounted for castoring. InFIG. 7 the wheels 70 are shown trailing thus indicating that theapparatus is moving in the direction of the arrow 72.

FIG. 8 shows one way in which the apparatus of any previous Figure canbe mounted so that it is held against the surface to be painted and sothat the gun as a whole may be manipulated with considerable facilityover a wide area, both as to vertical and horizontal passage over thesurface. The gun is attached to the structure of FIG. 8 by means of abush which slides on a rod 81. The gun is caused to traverse the rod 81by an air motor, omitted from the drawing for simplicity, spraying aswath of paint as it does so. The rod 81 is attached to two radius arms82 (only one of which is shown) which are connected by journals to theframe S3 which also carries, in bearings, the two shafts 84. Attached tothe ends of the shafts 84 are vacuum cups 85 (only two of which areshown). A hearing movement is imparted via a shaft 88 to the radius arms82 by means of a pneumatic motor 89, the torque reaction beingtransmitted from the motor casing to the frame 83.

In operation the device is placed on the surface to be painted and allfour vacuum cups 85 evacuated causing them to adhere strongly to thesurface. A torque is produced by the motor 89 in the arrowed directionand in consequence the spray gun is pressed against the surface. The gunis caused to traverse the length of the rod 81 and come to rest at oneend. If the'vacuum is released from vacuum cups 85C and 85D whilsttorque is maintained by the motor, the frame 83 will, because of torquereaction rotate about the shaft 88 and will so to speak, take one stepto the left (of the Figure). Reevacuating cups 85C and 85D will oncemore cause the device to be held rigidly to the surface and the movementof the spray gun restarted. The sprockets 86 and chain 87 cause the twovacuum cups which are taking the step to present their openings squarelyto the surface. By repetitive functioning of the vacuum system thedevice may be made to make along the surface to be painted.

The radius arms 82 may be in the form of a toggle linkage and may thuspermit the rod 81 to be angled in respect to the frame 83 and inconsequence may give improved mobility to the gun.

The whole of this device may be controlled both as to suction andstepping by any suitable type of pilot or electrically operated valves.

Although this method of temporary attachment of the gun apparatus to thesurface to be painted is given by way of example, it is to be understoodthat various other expedients may be used. We have previously mentionedthe possibility of using a propeller-like device 109 as shown in FIG. 9.Permanent or electromagnets 110 as shown in FIG. 1 may be used where thesurface to be painted is for example of mild steel.

Turning now to FIGS. 9 and 9A, a variant is illustrated which is in itsturn capable of being very considerably changed. In essence its purposeis first to economise in the required airflow and secondarily to reducethe amount of bubbling which may inconvenience the operator; further thedevice may have some use in removing lose particles from the surfaceabout to be painted. There is indicated a shield 90 with the margin ofits opening at 91. On a sliding bar such as at 92 which is mountedparallel with thelong dimension of the margin 91, there is mounted aflexible strip 93 which may be formed of bristles or of a resilientmaterial. Along the other dimension of the margin 91 is a similar barand strip, 95 and 96. The bars 92 and 95, can be moved on their guidesand thus bring the strips 93 and 96 into contact with the surface 97 tobe painted. When the spray is being moved upwards as indicated by thearrow in FIG. 9 the strip 93 is moved into a position where it acts,somewhat like a skirt of cushioncraft vehicle but actually in contactwith the surface 97 and therefore sealing the leading edge of the margin91 against outward leakage of air from the shield 90. Alternatively inFIG. 9A when the spray is being moved downwards the strip 96 is put incontact with the surface 97. The movements of the strips 93 and 96 arecontrolled in harmony with movement ofa guidewheel 98 or 99 which ismoved down to roll on the surface 97 according to the sense of directionof the passage of the apparatus. The wheels 98 and 99 are the equivalentof the wheels 32 in the previous Figures. It is unimportant whatinterconnection there is between the guidewheels and the sealing strips.By this device it will be seen that where the apparatus is being passedin one sense or the other of direction the leading edge is in effectsealed against the surface 97 whilst the trailing edge is clear. It isof course behind the leading edge that wet paint is deposited. The endportions of the shield 90 can either be left unsealed or may haveextensions of the seal 93 or 96 extending partially around such ends.FIG. discloses a further embodiment showing a plurality of shields 111and 112 each with spray nozzle and air supply means 151 and 152 so as toprovide a substantially uniform pattern of spray onto the surface.

The invention will have been seen to include not only a method forpainting or performing like functions under-water, but also apparatusfor carrying out such a method and various modifications thereof.

The paint selected to be used for underwater application by the sprayapparatus should be such as to set cure or dry by chemical reaction(e.g. as in the epoxy system); solvent loss,; or absorption of oxygenfrom the water to polymerise the film, perhaps aided by the air suppliedto purge the shield. The nature of the paint itself is believed to aidpenetration of the thin water film left on the surface; probably thishas to do with water solubility of one or more ingredients, andflushing-off of solvents may play a part. Such features may be ofaccount in making the selection.

We claim: 1. Method of coating a submerged surface by spraying with aliquid, comprising the steps of;

passing over the surface the margin of an opening which is of relativelyshort dimension in the direction of such passage and of relatively longdimension in the direction across such passage,

maintaining the margin so that at least its trailing edge of longerdimension in relation to the sense of direction of passage is spacedfrom the surface by a gap which leads from the opening of an otherwisewater-tight hollow shield,

supplying into the shield compressed air through its inlet at asufficient pressure and rate to keep the interior of the shield purgedof water whilst escaping through the gap,

and projecting the liquid to the surface from a source which is insidethe shield and spaced from the surface as a spray of droplets in asheet-like pattern corresponding in short and long dimensions to theopening but smaller, the spray of droplets being assisted in its passagetoward the opening by the compressed air,

the velocity of projection of the droplets and their mass being suchthat at least a majority of them penetrate the volume of intervening airmaintained within the shield and such film of water as there may be onthe surface so as to reach the surface and form thereon a continuousfilm, the gap between the surface and the margin of the opening beingmaintained so as to prevent water from entering the shield by the flowof compressed air passing through the gap from the shield.

2. Method according to claim 1 in which the compressed air is suppliedto the interior of the shield through a passage which surrounds thesource of liquid so that the general direction of air movement in theshield corresponds with that of the spray over substantially the samedistance.

3. Method according to claim 1 in which the said gap is maintained byurging the shield towards the surface and limiting its position by meansbearing against unsprayed area of the surface.

4. Method according to claim 3 in which the said means is adjustable soas to adjust the gap.

5. Method according to claim 3 in which the gap is maintained betweenthe trailing edge of the shield margin and the surface at least theleading edge of the margin being of yieldable material such as to slidein relatively airtight contact on the unsprayed surface.

6. Method according to claim 3 in which the positionlimiting means ischanged according to the sense of direction of passage over the surface.

7. Method according to claim 3 in which the positionlimiting meanscomprise a surface-bearing device arranged to one side of the shield (asrelated to its passage direction) and at least two other secondarybearing devices spaced from the opening of the shield in the path of theopening,

in which method one or other of the secondary bearing devices iscontrollably put into operation according to the sense of direction ofpassage whereby the alternative of such secondary devices is out ofcontact with newly-sprayed surface.

8. Method according to claim 3 in which the positionlimiting meansinclude wheels which are mounted for directional orientation and inwhich method the wheels are orientated so as to traverse the shield fromone passage traek to a further parallel track.

9. Method according to claim 1 in which the shield is urged towards thesurface by a thrust caused by propeller-like means.

10. Method according to claim 1 in which the shield is urged towards thesurface by magnetism.

11. Method according to claim 1 in which the shield so that its openingis lower than its main interior voltime, so that it acts as adiving-bell" to retain a pocket of air even if the air suppply thereintois interrupted.

12. Method according to claim 1 in which the pressure of the air supplyis controlled so as to be compatible with the depth at which the methodis performed.

13. Method according to claim 1 in which the source inside the shieldcomprises a plurality of dropletspraying nozzles spaced across thedirection of passage, the liquid being supplied to such nozzles inparallel during the passage.

14. Method according to claim 1 in which the shield is supported by astructure held against the surface and which is adapted to traverse theshield along a first passage track, thereafter to shift the shield by apredetermined dimension in a direction transverse to said track, and totraverse the shield along a second passage track

1. METHOD OF COATING A SUBMERGED SURFACE BY SPRAYING WITH A LIQUID,COMPRISING THE STEPS OF; PASSING OVER THE SURFACE THE MARGIN OF ANOPENING WHICH IS OF RELATIVELY SHORT DIMENSION IN THE DIRECTION OF SUCHPASSAGE AND OF RELATIVELY LONG DIMENSION IN THE DIRECTION ACROSS SUCHPASSAGE, MAINTAINING THE MARGIN SO THAT AT LEAST ITS TRAILING EDGE OFLONGER DIMENSION IN RELATION TO THE SENSE OF DIRECTION OF PASSAGE ISSPACED FROM THE SURFACE BY A GAP WHICH LEADS FROM THE OPENING OF ANOTHERWISE WATER-TIGHT HOLLOW SHIELD, SUPPLYING INTO THE SHIELDCOMPRESSED AIR THROUGH ITS INLET AT A SUFFICIENT PRESSURE AND RATE TOKEEP THE INTERIOR OF THE SHIELD PURGED OF WATER WHILST ESCAPING THROUGHTHE GAP, AND PROJECTING THE LIQUID TO THE SURFACE FROM A SOURCE WHICH ISINSIDE THE SHIELD AND SPACED FROM THE SURFACE AS A SPRAY
 2. Methodaccording to claim 1 in which the compressed air is supplied to theinterior of the shield through a passage which surrounds the source ofliquid so that the general direction of air movement in the shieldcorresponds with that of the spray over substantially the same distance.3. Method according to claim 1 in which the said gap is maintained byurging the shield towards the surface and limiting its position by meansbearing against unsprayed area of the surface.
 4. Method according toclaim 3 in which the said means is adjustable so as to adjust the gap.5. Method according to claim 3 in which the gap is maintained betweenthe trailing edge of the shield margin and the surface at least theleading edge of the margin being of yieldable material such as to slidein relatively airtight contact on the unsprayed surface.
 6. Methodaccording to claim 3 in which the position-limiting means is changedaccording to the sense of direction of passage over the surface. 7.Method according to claim 3 in which the position-limiting meanscomprise a surface-bearing device arranged to one side of the shield (asrelated to its passage direction) and at least two other secondarybearing devices spaced from the opening of the shield in the path of theopening, in which method one or other of the secondary bearing devicesis controllably put into operation according to the sense of directionof passage whereby the alternative of such secondary devices is out ofcontact with newly-sprayed surface.
 8. Method according to claim 3 inwhich the position-limiting means include wheels which are mounted fordirectional orientation and in which method the wheels are orientated soas to traverse the shield from one passage track to a further paralleltrack.
 9. Method according to claim 1 in which the shield is urgedtowards the surface by a thrust caused by propeller-like means. 10.Method according to claim 1 in which the shield is urged towards thesurface by magnetism.
 11. Method according to claim 1 in which theshield is arranged and held positioned relatively to the surface so thatits opening is lower than its main interior volume, so that it acts as a''''diving-bell'''' to retain a pocket of air even if the air suppplythereinto is interrupted.
 12. Method according to claim 1 in which thepressure of the air supply is controlled so as to be compatible with thedepth at which the method is performed.
 13. Method according to claim 1in which the source inside the shield comprises a plurality ofdroplet-spraying nozzles spaced across the direction of passage, theliquid being supplied to such nozzles in parallel during the passage.14. Method according to claim 1 in which the shield is supported by astructure held against the surface and which is adapted to traverse theshield along a first passage track, thereafter to shift the shield by apredetermined dimension in a direction transverse to said track, and totraverse the shield along a second passage track parallel to the first.